1. Field of the Invention
The present invention relates generally to a method and apparatus for enhancing exhaust gas recirculation efficiency on a combustion engine, and more particularly to a pulse reflector that enhances the exhaust gas recirculation efficiency and reduces engine emissions.
2. Background
The demand for cleaner burning internal combustion engines has continued to increase in recent years culminating from both a general desire to reduce emissions and from increasingly strict environmental legislation. The concern regarding combustion engines stems from the fact that they, as a result of operation, typically produce products in the emitted exhaust that can be harmful to the environment. Common examples of these types of products include nitrous oxides, carbon monoxide, carbon dioxide, and various hydrocarbons. These products not only pose harm to the environment, but some represent wastefulness in that they have not been fully burned and have a capacity for releasing additional stored potential energy. Several methods have been developed to reduce these emissions, such as modifying the design of the combustion chamber and adjusting the timing of injecting fuel into the engine.
Current environmental standards and future expected legislation have made the issue of emissions a special concern for the diesel utilizing industries. Fuel economy has always been an important goal of these industries, and in particular, the diesel-powered transport businesses. At least partially in answer to these criteria, one method for reducing emissions from a diesel engine has been developed, and is achieved by providing the engine with an exhaust gas recirculation system, commonly known as an EGR system. The present invention is directed to such an EGR system.
An EGR system recirculates a portion of exhaust gas back into the air intake side of a combustion engine. This recirculation not only allows for further combustion of the exhaust products, but it also selectively advantageously dilutes the incoming air/fuel in the cylinders. It is known that formation of certain pollutants, such as NOx, in a diesel engine is exponentially proportional to the temperature in the combustion chamber. By lowering the combustion temperature, these NOx emissions are successfully reduced.
An EGR system recirculates at least a portion of the exhaust gas by joining the exhaust system with the air intake system by means of a special return path. As expected, the emitted exhaust gas is rather high in temperature. The EGR system seeks to dilute the incoming air/fuel charge and preferably lower the combustion temperature. Thus, an EGR cooler preferably cools the exhaust gas before it is returned to the air intake system.
A controllable valve regulates the amount of exhaust gas entering into the EGR bypass. A control unit will monitor and vary the degree of opening of the controllable valve depending on several parameters such as current operating conditions of the engine and the temperature of the coolant in the EGR cooler. Opening the controllable valve permits exhaust gases to recirculate back to the engine air-intake, but if there is insufficient pressure within the exhaust system itself, flow of exhaust gases through this valve will not be achieved. In other words, the pressure of the exhaust gases in the exhaust system must, at least occasionally, exceed the pressure at the intake side of the engine, a pressure imbalance is created that drives the exhaust gases through the EGR system. This pressure differential drives conventional EGR systems, and produces a corresponding decrease in emissions. Without this drive pressure, the EGR system will not operate at all, or at least not efficiently.
The industry has therefore sought to address the problem of insuring a sufficient amount of drive pressure within the exhaust side of the engine. For example, turbo units incorporating variable turbine geometry can be used toward, at least intermittently, this purpose. By varying the angle of the turbine blades, a sufficiently high pressure can be built up on the exhaust side of the engine. This solution has, however, the disadvantage that it results in deterioration of the engine's gas-exchange and heat balance, which in turn makes the engine less efficient. Another method selectively isolates each cylinder and inserts a shunt valve, which also works as a metering valve, to control the amount of exhaust gases required at that particular point in the system. However, by only using exhaust gases from one cylinder at a time, the recirculated exhaust gas is not distributed evenly into the intake system. The exhaust gases are emitted as high-pressure pulses, not a continuous flow, and thus the pulses distribute unevenly to the cylinders at the intake side of the engine. If there is too great a range in the amount of exhaust gases fed into the cylinders, there will be an insufficient reduction in the emissions. Thus there is a need in the industry to provide a high amount of drive pressure, or over-pressure in the exhaust system to enhance the efficiency of an EGR system leading to a decrease in emissions.
The present invention provides a simple, elegant solution to effectively raise the drive pressure in the EGR system thereby enhancing the efficiency of the engine and reducing emissions.